Among various cleaning solvents, chlorofluorocarbon and chlorine-based solvents have been widely used heretofore. However, the use of these cleaning solvents has been regulated because of environmental problems that have risen in recent years such as the destruction of the ozone layer. Under these circumstances, a composition mainly consisting of normal propyl bromide (aka: n-propyl bromide, 1-bromopropane; hereinafter it may also be referred to simply as NPB) has been proposed as a new cleaning solvent in place of chlorofluorocarbon and chlorine-based solvents. The KB value of n-propyl bromide is about 125 which is relatively high. It is excellent at degrease cleaning and it also has a nonflammable or flame-retardant property without a flash point. Accordingly, n-propyl bromide is not considered as a hazardous material, and is safe and easy to handle. Moreover, neither fluorine-based solvents nor chlorine-based solvents are included therein at all. From these reasons, n-propyl bromide is drawing attention as being friendly to the environment at present.
However, n-propyl bromide has a disadvantage that a decomposition reaction is likely to take place which is induced by various metals such as aluminum, zinc, iron and copper. The decomposition reaction of n-propyl bromide is caused by the contact with a metal. The reaction varies according to the kind of metal, and is significant especially in the case of aluminum. The decomposition reaction progresses at a considerably slow rate at normal temperature. On the other hand, under a heated condition, the decomposition progresses in a chain reaction manner while generating hydrogen bromide, and eventually aluminum is vigorously corroded in some cases. Accordingly, in a case where n-propyl bromide is used, e.g., for cleaning various metallic components, it is necessary to stabilize n-propyl bromide so that n-propyl bromide can be prevented from corroding objects subject to cleaning and cleaning apparatuses while suppressing the decomposition reaction induced by various metals, particularly aluminum.